Mysterious Sound Recorded in Mariana Trench Believed to be from Minke Whales

A strange sound in the Mariana Trench notable for its complexity likely represents the discovery of a new minke whale call, says a team of marine researchers from Cornell University and Oregon State University.

Minke whale. Image credit: Len Joh / CC BY-ND 2.0.

Dubbed the ‘Western Pacific Biotwang,’ this call is the subject of a recently published paper in the Journal of the Acoustical Society of America.

Lasting between 2.5 and 3.5 seconds, the five-part call includes deep moans at frequencies as low as 38 Hz and a metallic finale that pushes as high as 8,000 Hz.

“It’s very distinct, with all these crazy parts. The low-frequency moaning part is typical of baleen whales, and it’s that kind of twangy sound that makes it really unique. We don’t find many new baleen whale calls,” said study lead author Dr. Sharon Nieukirk, a researcher in the Cooperative Institute for Marine Resources Studies at Oregon State University.

The new call was recorded via passive acoustic ocean gliders in an area east of Guam.

“In fall 2014 and spring 2015, passive acoustic data were collected via autonomous gliders east of Guam in an area that included the Mariana Trench Marine National Monument,” the researchers said.

“A short, complex sound was recorded that features a 38 Hz moan with both harmonics and amplitude modulation, followed by broad-frequency metallic-sounding sweeps up to 7.5 kHz.”

“This sound was recorded regularly during both fall and spring surveys.”

The Western Pacific Biotwang most closely resembles the so-called ‘Star Wars’ sound produced by dwarf minke whales on the Great Barrier Reef off the northeast coast of Australia.

The complex structure of the sound, the frequency sweep, and the metallic nature of the final part of this call are all very similar to characteristics of Star Wars calls.

“Minke whales are baleen whales – meaning they feed by using baleen plates in their mouths to filter krill and small fish from seawater – and live in most oceans,” the scientists said.

“They produce a collection of regionally specific calls, which in addition to the Star Wars call include ‘boings’ in the North Pacific and low-frequency pulse trains in the Atlantic.”

“The species is the smallest of the baleen whales, doesn’t spend much time at the surface, has an inconspicuous blow, and often lives in areas where high seas make sighting difficult. But they call frequently, making them good candidates for acoustic studies.”

Baleen whale calls are often related to mating and heard mainly during the winter, yet the Western Pacific Biotwang was recorded throughout the year.

“If it’s a mating call, why are we getting it year round? That’s a mystery,” Dr. Nieukirk said.

“We need to determine how often the call occurs in summer versus winter, and how widely this call is really distributed.”